Abstract Detail

Paleobotany

Allen, Sarah [1].

Reconstructing the local vegetation of the Early Eocene Blue Rim site of southwestern Wyoming—incorporating new data from fossil woods.

The Blue Rim escarpment of the early Eocene (~49.5 Ma) Bridger Formation in southwestern Wyoming preserves fossils of leaves, flowers, fruits, seeds, permineralized wood, and dispersed pollen. Each component of the flora provides a slightly different view of the diversity and environment, but taken as a whole, a more complete picture of the landscape is revealed. Fossil wood specimens, including occasional in situ stumps, have been recovered from multiple Blue Rim localities. A single conifer specimen of Pinaceae had large uniseriate tracheary pits and intercellular canals. This find is significant because no other conifer macrofossils have been found at Blue Rim, even though dispersed pinaceous pollen is common. Angiosperm woods include diffuse porous types with affinities to Fabaceae, Canellaceae, and Anacardiaceae. The fabaceous wood lacks storied structure and is characterized by paratracheal axial parenchyma ranging from vasicentric, to aliform, and confluent. The specimen assigned to Canellaceae, can be distinguished as the only Blue Rim wood with scalariform perforation plates, predominately uniseriate rays, and mostly solitary vessels. To date, no leaves or other fossils of Fabaceae or Canellaceae have been documented from Blue Rim. Numerous specimens with radial canals and regular prismatic crystals comprise a wood type similar to or perhaps representative of the fossil genus Edenoxylon, assignable to Anacardiaceae. Fruits and likely leaves of Anacardiaceae have been recognized at Blue Rim. The Blue Rim wood assemblage has significantly lower taxonomic diversity than the leaves, reproductive structures, and dispersed pollen. At least twenty morphotypes of both leaves and reproductive structures have been recovered including Populus, Macginitiea, and Landeenia. While not all macrofossils have been examined, numerous taxa (e.g., Ephedra, Chenopodium, Alnus, Carya, Tilia, Asteraceae) are present only in the dispersed palynoflora and may be more representative of the regional rather than the local flora. Nine wood specimens whose full diameter (ranging from 20–55 cm) could be measured were used to estimate tree height. These trees reached ~16–28 m tall and likely represent some of the larger trees on the landscape. Self-supporting taxa would have been essential for climbers such as Iodes, Vitis, and Lygodium present in the same flora. Characters observed in the Blue Rim woods including diffuse porosity, absent or indistinct growth rings, and rare scalariform perforation plates suggest climate conditions were warm with limited seasonality. These findings are in agreement with paleoclimate estimates from leaf physiognomic methods and the presence of frost-intolerant taxa like Phoenix.

1 - University of Florida & Florida Museum of Natural History, Department of Biology, P.O Box 118525, Gainesville, FL, 32611, USA

Keywords:
fossil wood
Eocene
Bridger Formation
Wyoming
Pinaceae
Canellaceae
Fabaceae
Anacardiaceae.

Presentation Type: Oral Paper
Session: 5, Paleobotany Student Awards
Location: 204/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 10:30 AM
Number: 5009
Abstract ID:212
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award